Imaging apparatus and imaging signal correcting method

ABSTRACT

An imaging apparatus includes: a lens mount section; an imager having an imaging plane on which an image having an image height obtained through a lens device mounted to the lens mount section is formed; an imaging process section correcting transverse chromatic aberration of an imaging signal obtained by the imager; and a control section determining an imager size in accordance with the diameter of the lens device mounted to the lens mount section and correcting a correction coefficient for the correction of transverse chromatic aberration at the imaging process section according to the size thus determined.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging apparatus such as a videocamera and an imaging signal correcting method used in such an imagingapparatus. In particular, the invention relates to such a technique usedin lens-interchangeable imaging apparatus.

2. Description of the Related Art

Some imaging apparatus such as video cameras performs correct transversechromatic aberration of imaging signals obtained by imaging objectsusing the imagers. Correction of transverse chromatic aberration is tocorrect signals at each pixel position (in particular, signals ofneighboring pixels) in each frame of an imaging signal based oncharacteristics information concerning aberration of the lens attachedto the imaging apparatus of interest.

Correction of transverse chromatic aberration makes it possible toprevent deterioration of image quality attributable to lens aberration,whereby imaging can be performed satisfactorily.

An example of correction of transverse chromatic aberration is describedin JP-A-2008-96907 (Patent Document 1). In Patent Document 1, alens-interchangeable imaging apparatus is described. Lenscharacteristics information for correcting transverse chromaticaberration is stored in lens devices, and the imaging apparatus readsout the stored lens characteristics information to perform a correctionprocess. The configuration described in Patent Document 1 allowstransverse chromatic aberration to be properly corrected even in alens-interchangeable imaging apparatus.

SUMMARY OF THE INVENTION

Lens devices which can be mounted to a lens-interchangeable imagingapparatus such as a video camera have fixed diameters. For example,referring to typical sizes of lens devices for video cameras, there arelens devices for ⅔-inch imagers and lens devices for ½-inch imagers. A⅔-inch imager is an imager having an imaging plane with a diagonallength of ⅔ inches.

Lens devices of different sizes have respective lens mount sectionshaving different diameters, and the size of a lens to be mounted to eachvideo camera is fixed.

Although an imaging system has a fixed size as thus described, lensdevices having different diameters can be mounted to the imagingapparatus using a conversion adaptor for converting the size of a lensmount section. Specifically, an imaging apparatus which is originallydesigned to allow a ½-inch lens device to be mounted thereto can beadapted to a ⅔-inch lens device having a greater diameter using aconversion adaptor. Since lenses of different sizes can be mounted usinga conversion adaptor as thus described, existing lenses possessed by auser can be effectively used.

When lens devices having different lens diameters are mounted to animaging apparatus, a problem arises in that transverse chromaticaberration as described above may not be properly corrected. Correctionof transverse chromatic aberration is a process of correcting chromaticaberration which varies depending on pixel positions within an imageframe to obtain an imaging signal having no chromatic aberration. When alens attached to an imager is changed to another lens having a differentdiameter, the image frame of an image height formed by the lens may bedifferent from the image frame of a signal imaged by the imager.

FIG. 5 shows a reason why correction of transverse chromatic aberrationis required. Preferably, an image is formed through a lens L in aposition which remains unchanged regardless of the color of the imagewhen the lens L is an ideal lens. In practice, however, images in red(R), blue (B), and green (G) are formed in positions which are slightlydifferent from each other. In particular, shifts of great amounts occurat peripheral regions apart from the central axis of the lens, as shownin FIG. 5. Such shifts between the positions of colors depend on thecharacteristics of the lens used, and completely different shifts occurwhen a lens of a different configuration is used.

In a transverse chromatic aberration correcting process, chromaticaberration is corrected by converting pixel positions such that thepositions of pixels in three primary colors which are shifted whenimaged will coincide with each other. Specifically, correction iscarried out such that a pixel signal in an imaging position of red (R),an imaging signal in an imaging position of blue (B), and an imagingsignal in an imaging position of green (G) as shown in FIG. 5 will beconverted into pixel signals in the same position.

When a ½-inch lens device mounted to an imaging apparatus is replacedwith a ⅔-inch lens device as described above, an object is imaged in aposition that is shifted toward a telephoto side compared to a positionwhere the object is imaged by a ⅔-inch imaging apparatus. Therefore,even when the imaging apparatus acquires a correction coefficient forcorrecting transverse chromatic aberration set for the ⅔-inch lensdevice mounted to the apparatus as thus described, the imaging apparatuswill make an erroneous strong correction because of a difference betweenimage frames of the lenses. Thus, when a lens device is mounted toreplace another lens device of a different size, the degradation ofimage quality can occur.

Under the circumstance, it is desirable to allow an imaging apparatus toperform an imaging process properly regardless of the size of a lensmounted to the apparatus.

According to an embodiment of the invention, transverse chromaticaberration of an imaging signal obtained through an imager is correctedusing a correction coefficient specific to a lens device. The diameterof a lens device mounted to a lens mount section is determined, and acorrection coefficient for correcting transverse chromatic aberration iscorrected according to the determined size to execute a correctionprocess.

As a result, when a lens device is replaced with another lens devicehaving a different lens diameter, a correction coefficient forcorrecting transverse chromatic aberration of an imaging signal iscorrected to allow transverse chromatic aberration to be corrected usinga proper correction coefficient.

According to the embodiment of the invention, transverse chromaticaberration can be corrected using a proper correction coefficientregardless of the lens diameter of the lens device mounted to theimaging apparatus of interest, which is advantageous in that imaging canbe performed with transverse chromatic aberration properly correctedregardless of lens diameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is illustrations showing an exemplary system configuration of acamera apparatus and lens devices according to an embodiment of theinvention;

FIG. 2 is a block diagram of the camera apparatus according to theembodiment of the invention showing an exemplary configuration thereof;

FIG. 3 is a flow chart showing an example of a process of setting acorrection coefficient of the camera apparatus according to theembodiment of the invention;

FIG. 4 is an illustration showing a position to be corrected accordingto the embodiment of the invention; and

FIG. 5 is an illustration showing a reason why correction of transversechromatic aberration is required.

DESCRIPTION OF PREFERRED EMBODIMENTS

Details of an embodiment of the invention will now be described in theorder listed below.

1. Exemplary System Configuration of the Embodiment (FIG. 1)

2. Exemplary Configuration of Imaging Apparatus of the Embodiment (FIG.2)

3. Description of a correction coefficient setting process (FIGS. 3 and4)

[1. Exemplary System Configuration of the Embodiment]

An exemplary system configuration of the embodiment of the inventionwill now be described with reference to FIG. 1.

As shown in FIG. 1, a camera apparatus 10, which is an imagingapparatus, includes a lens mount section 11, and lens devices can bemounted to the lens mount section 11 to allow lenses to be freely usedon an interchangeable manner. The lens mount section 11 is a mountsection for mounting a ½-inch type lens device 30.

The ½-inch type lens device 30 includes a lens disposed in a lens barrel31 and a mount section 32 provided at a rear end thereof. The term“½-inch type” indicates that lens device is a lens device to be usedwith a camera apparatus whose imager has an imaging plane with adiagonal length of ½ in. The mount section 32 is a mount section whichis sized to be fitted to the mount section 11 of the camera apparatus.The lens device 30 includes a memory 33 provided in the lens barrel 31,and data specific to the lens device 30 are stored in the memory 33.Lens type data and data of various correction coefficients such as acorrection coefficient for correcting transverse chromatic aberration ofthe lens are stored as the data specific to the lens device 30.

As shown in FIG. 1, the lens mount section 11 of the camera apparatus 10is configured such that a ⅔-inch type lens device 40 can be mounted tothe mount section using a conversion adaptor 50. The term “⅔-inch type”indicates that the ⅔-inch type lens device 40 is a lens device to beused with a camera apparatus whose imager has an imaging plane with adiagonal length of ⅔ in. In general, a lens device of this type has alens diameter greater than that of a ½-inch type lens device.

The ⅔-inch type lens device 40 includes a ⅔-inch type lens mount section42 provided at a rear end of a lens barrel 41. The lens device 40includes a memory 43 provided in the lens barrel 41, and data specificto the lens device 40 are stored in the memory 43. Lens type data anddata of various correction coefficients such as a correction coefficientfor correcting transverse chromatic aberration of the lens are stored asthe data specific to the lens device 40.

The conversion adaptor 50 includes a lens mount section 51 to which a⅔-inch type lens device is to be mounted and a main body mount section52 for mounting the adaptor to the apparatus main body which is designedto allow mounting of a ½-inch type les device. The conversion adaptor 50has the function of repeating the data stored in the memory 43 of thelens device 40 mounted thereto to the main body of the imaging apparatusconnected to the main body mount section 52.

[2. Exemplary Configuration of Imaging Apparatus of the Embodiment]

An internal configuration of the camera apparatus 10 or the imagingapparatus will now be described with reference to FIG. 2.

The camera apparatus 10 includes an imager 12. The lens mount section 11shown in FIG. 1 is provided in front of the imager 12 to allow the lensdevice 30 to be mounted directly to the apparatus or to allow the lensdevice 40 to be mounted through the conversion adaptor 50.

When an image having an image height obtained through the lens devicethus mounted is formed on an imaging plane of the imager 12, an imagingprocess is performed to obtain an imaging signal according to the imageheight of the image formed as thus described. The imager 12 is an imagerwhose imaging plane has a size adapted to a ½-inch type lens device.Various types of imagers such as CCD imager sensors and CMOS imagesensors may be used as the imager 12.

The imaging signal is read out by a readout circuit 13 connected to theimager 12, and the imaging signal read out is supplied to an imagingprocess section 14. The imaging process section 14 may perform variouscorrection processes on the imaging signal to correct the signal. Forexample, a transverse chromatic aberration correcting process isperformed. A peripheral dimming correcting process may alternatively beperformed. Such a correction process at the imaging process section 14is executed under control exercised by a control section 20. The controlsection 20 communicates with the lens device mounted to the apparatusthrough an interface section 19 which is a communication section toacquire a correction coefficient required for the correction processfrom the memory 33 or 43 of the lens device. A transverse chromaticaberration correcting process is performed using the correctioncoefficient thus acquired under control exercised by the control section20. When the control section 20 determines that the lens device mountedis the ⅔-inch type lens device, a correction process is performed tocorrect the correction coefficient acquired from the memory of the lensdevice, and a correction calculation process is performed using thecorrected correction process. Data required for the correctioncalculation process are stored in advance in a memory 21.

The imaging signal is supplied to a video conversion section 15 afterbeing corrected by the imaging process section 14 to convert it into avideo signal in a predetermined format, and the video signal obtained asa result of the conversion is supplied to a display section 16 anddisplayed on the same. The video signal obtained by the video conversionsection 15 is also supplied to a recording section 17 and recordedtherein. Further, the video signal obtained by the video conversionsection 15 is supplied to an output section 18 and output from theapparatus.

The camera apparatus 10 includes an operation section 22, and a user canoperate the operation section 22 makes various settings. When themounted lens device has no memory incorporated therein, a menu screen orthe like may be displayed to allow a user to select a correctioncoefficient on the screen by operating the operation section 22. Theselected correction coefficient may be stored in the memory 21.

[3. Description of a Correction Coefficient Setting Process]

A description will now be made with reference to the flow chart in FIG.3 on a process of setting a correction coefficient included in thetransverse chromatic aberration correcting process performed by theimaging process section 14.

First, the control section 20 determines whether the lens device mountedto the camera apparatus 10 is the ½-inch type lens device or the ⅔-inchtype lens device (step S11). For example, the determination process isperformed when the power supply of the camera apparatus 10 is turned on.The process may alternatively be performed when a lens replacingoperation is detected.

For example, when the lens type number can be read out from the memory(memory 33 or 43) of the lens device mounted, the determination may bemade from such data. When detection can be carried out to determinewhether the conversion adaptor 50 is mounted or not, the determinationof the lens device type can be made based on whether the conversionadaptor 50 is mounted or not. Further, when the determination cannot beautomatically made as thus described, the sizes of the lenses may beregistered and stored in the memory 21 through user operations on theoperation section 22 when the lenses are mounted, and the determinationof the lens device type may be made by reading out the registered lenssize data.

When it is determined at step S11 that the mounted device is the ½-inchtype lens device, the control section 20 determines whether a correctioncoefficient Ai for correcting transverse chromatic aberration can beacquired from the mounted lens device or not (step S12). When it isdetermined that a correction coefficient Ai for correcting transversechromatic aberration can be acquired, the interface section 19 reads outthe correction coefficient Ai of interest from the memory 33 of the lensdevice, and the control section 20 sets the correction coefficient Aithus reads out as a coefficient to be used for correction (step S13).

When a correction coefficient Ai for correcting transverse chromaticaberration cannot be acquired from the lens device at step S12 (or whenthe lens includes no memory), a correction coefficient Ai may be set bya user operation (step S14).

When it is determined at step S11 that the mounted device is the ⅔-inchtype lens device, the control section 20 determines whether a correctioncoefficient Ai for correcting transverse chromatic aberration can beacquired from the mounted lens device or not (step S15). When it isdetermined that a correction coefficient Ai for correcting transversechromatic aberration can be acquired, the interface section 19 reads outthe correction coefficient Ai of interest from the memory 43 of the lensdevice. The acquired correction coefficient Ai is converted into acorrection coefficient Ai′ for a ½-inch type imager (step S16). Thecontrol section sets the correction coefficient Ai′ obtained by theconversion as a coefficient to be used for correction (step S17).

When a correction coefficient Ai for correcting transverse chromaticaberration cannot be acquired from the lens device at step S15 (or whenthe lens includes no memory), the process proceeds to step S14 to set acorrection coefficient Ai through a user operation.

When the correction coefficient Ai or Ai′ is set at step S13, S14, orS17, the process proceeds to step S18 at which the imaging processsection 14 performs a transverse chromatic aberration correcting processusing the correction coefficient Ai or Ai′ thus set (step S18).

An example of correction of transverse chromatic aberration will now bedescribed.

Correction of transverse chromatic aberration is performed according toExpression (1) shown below.

$\begin{matrix}{Y = {\sum\limits_{i = 0}^{n}{AiX}^{i}}} & (1)\end{matrix}$

In Expression (1), Y represents the amount of a correction [μm] made onan imager; X represents a distance [μm] from the center of the imager;and Ai represents a correction coefficient. At the imaging processsection 14, the correction coefficient Ai is multiplied by a coefficientαi to obtain another correction coefficient ai in order to convert thecorrection represented by a distance into a pixel position. That is, acoefficient ai=α1·Ai is obtained, and transverse chromatic aberration iscorrected using the coefficient ai. Correction is carried out usingdifferent characteristics for each primary color signal.

When the ½-inch type lens device is mounted, correction is carried outas described above using the correction coefficient Ai read out from thelens device as it is.

When the ⅔-inch type lens device is mounted, the correction coefficientAi is further multiplied by a conversion coefficient Ui. That is, acoefficient ai=Ui·αi·Ai is obtained, and transverse chromatic aberrationis corrected using the coefficient ai.

Specifically, the conversion coefficient Ui equals ( 8/11)^(i) becausethe ½-inch imager has a diagonal size of about 8 mm and the ⅔-inch imagehas a diagonal size of about 11 mm.

Let us assume that the ½-inch imager has an effective image frame V1 andthat the ⅔-inch imager has an effective image frame V2, as shown in FIG.4. When an imaging signal is corrected as thus described, a correctionapplied to a pixel Z2 at a corner of the image frame V2 is not appliedas it is to a pixel Z1 at a corner of the image frame V1. In thisexample, correction is carried out with the difference between the sizesof the image frames corrected. Therefore, correction can be properlycarried out even when lens devices having different sizes are used.

A correction process for correcting transverse chromatic aberration hasbeen described above, and correction of peripheral dimming may becarried out using a similar process. Specifically, a correctioncoefficient for correcting peripheral dimming may be acquired from alens device, and the acquired correction coefficient may be correctedaccording to the size of the lens. Unlike the correction of transversechromatic aberration, the correction of peripheral dimming is similarlyperformed regardless of colors.

The sizes of imagers in the above description of the embodiment aremerely shown as examples, and the invention is not limited to suchexamples. For example, lenses of other sizes such as a lens for a ⅓-inchtype imager may be used. Different correction coefficients may beprovided to accommodate lenses of three or more sizes, respectively.

While correction of transverse chromatic aberration and correction ofperipheral dimming has been described above, other characteristics of animaging signal may be corrected using a similar process as long as thecorrection is carried out based on lens characteristics.

While the above-described embodiment is an example of the application ofthe invention to a video camera as an imaging apparatus, the inventionmay be applied to other types of lens-interchangeable imaging apparatussuch as electronic still cameras.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2010-088960 filedin the Japan Patent Office on Apr. 7, 2010, the entire contents of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An imaging apparatus which can attach aninterchangeable lens comprising: a lens mount section configured tomount a plurality of lens devices of different sizes thereto, each lensdevice including a memory storing data including at least lens type dataand a correction coefficient for correcting transverse chromaticaberration specific to the lens device; an imager having an imagingplane on which an image having an image height obtained through a lensdevice mounted to the lens mount section is formed; an imaging processsection configured to correct transverse chromatic aberration of animaging signal obtained by the imager; and a control section configuredto (a) determine an imager size in accordance with a diameter of thelens device mounted to the lens mount section based on the lens typedata stored in the memory of the mounted lens device and (b) correct thecorrection coefficient, output from the memory, for the correction oftransverse chromatic aberration at the imaging process section accordingto the imager size thus determined only when the lens device is mountedto the lens mount section via a conversion adaptor.
 2. An imagingapparatus according to claim 1, comprising a communication sectionconfigured to communicate with the lens device mounted to the lens mountsection, wherein the control section determines the size from data heldin the lens obtained through communication carried out by thecommunication section.
 3. An imaging apparatus according to claim 2,wherein the control section acquires data of a correction coefficientheld in the lens device through communication carried out by thecommunication section; and the acquired correction coefficient data isconverted based on the determined size to perform the correction oftransverse chromatic aberration using the converted correctioncoefficient.
 4. An imaging apparatus according to claim 1, wherein theimaging process section performs correction of peripheral dimming of theimaging signal based on a correction coefficient for peripheral dimmingspecific to the lens device.
 5. An image processing method for an imageapparatus which can attach an interchangeable lens comprising the stepsof: correcting transverse chromatic aberration of an imaging signalobtained through an imager using a correction coefficient specific to alens device based on data including at least lens type data and acorrection coefficient for correcting transverse chromatic aberrationspecific to the lens device, the data is stored in a memory of the lensdevice mounted to a lens mount section, the lens amount section capableof mounting a plurality of lens devices of different sizes; determiningan imager size in accordance with a diameter of the lens device mountedto the lens mount section based on the lens type data stored in thememory of the lens device; and correcting the correction coefficient,output from the memory of the lens device, according to the imager sizedetermined at the determination step and exercising control to executethe correction process only when the lens device is mounted to the lensmount section via a conversion adaptor.